1. Field of the Invention
This invention relates to an optical connector, such as an FC optical connector defined in Japanese Industrial Standard (JIS) C 5970, for performing positioning around an axial direction at the time of connection to a receive-side optical connector, such as an optical connector adaptor.
2. Description of the Related Art
FIG. 7 shows one example of the constitution of a conventional optical connector of this type (in this example, an FC optical connector). The optical connector 1 comprises a substantially cylindrical frame 2, a sleeve-like stopper 3 which is connected to the frame 2, a boot 4 which is attached to the stopper 3, a coupling nut 6 in which the frame 2 is rotatably inserted through, a spring 7 which is accommodated inside the frame 2, and a ferrule 8 which is inserted through the frame 2. In addition, the stopper 3, the boot 4, and holding parts incorporated inside the stopper 3, comprises a holding section 5 which holds an unillustrated optical fiber in which the top thereof being stored in the ferrule 8, and prevents the moving backward of the optical fiber from the optical connector 1 (to the left of FIG. 7).
The ferrule 8 forms a cylindrical shape with a flange section 9 at its rear end, and has four meshing grooves 10 provided in the outer peripheral face of the flange section 9 at intervals of 90 degrees. The meshing grooves 10 are shaped so as to mesh with meshing pieces 11, protruding to the inside of the frame, in order to position the ferrule 8 when it is inserted through the frame 2, and consequently, after centering (also termed “adjusting”) as explained later, the meshing grooves 10 are selectively inserted and engaged with the meshing pieces 11, thereby achieving positioning of the ferrule 8 around an axial direction.
The ferrule 8 can move slightly along the axial direction with the meshing pieces 11 and meshing grooves 10 meshed together, and compresses the spring 7 when the ferrule 8 is pushed toward the rear side of the optical connector 1. The spring 7 generates a thrusting force against the ferrule which faces the other ferrule when two optical connectors are connected. Furthermore, an unillustrated stopper stops the ferrule 8 from flying out of the frame 2 toward the front of the optical connector 1.
A male screw section 12 is provided at the rear side of the outer peripheral face of the frame 2; a female screw section 13 is provided in the rear side of the coupling nut 6 and engages with the male screw section 12. In this example, the female screw section 13 is provided in the inner peripheral face of an inwardly-protruding section 14 at the rear side of the coupling nut 6. Furthermore, the inner diameter of the coupling nut 6 at the tip side thereof is sufficiently larger than the outer diameter of the frame 2; a female screw section 15 is provided in the inner peripheral face of the tip side of the coupling nut 6, and engages with a male screw section which is provided in the outer peripheral face of a sleeve section 22a (see FIG. 9) of an optical connector adaptor 22 which will be explained later.
A bump 16 is provided in the outer peripheral face of the frame 2 nearer to the tip side than the male screw section 12. The bump 16 extends along the rim of the frame 2, contacts the protruding section 14 of the coupling nut 6 with a washer 17 therebetween, and prevents the coupling nut 6 from slipping out of the frame 2.
A key ring 18 is attached over the outer peripheral face of the frame 2 nearer to the tip side than the bump 16. As shown in FIG. 8, the key ring 18 is made of resin or metal, and has a key ring main body 19, which has been made discontinuous by cutting a notch therein, a positioning projection 20 (hereinafter termed “key”) which extends along one side of the key ring main body 19, and a pair of projections 21, which extend along the opposite side of the key ring main body 19. The projections 21 and the key 20 are provided at a right-angled position along the rim of the key ring 18.
The key ring 18 of this constitution is engaged and provided over the frame 2, by facing the lips 21 (not shown in FIG. 7) to the bump 16 side, so that the key 20 faces the tip side of the frame 2. The projections 21 of the key ring 18 engage with engagement portions (not shown in figure), provided in the bump 16 or the outer peripheral face of the frame 2, thereby positioning the key ring 18 around the axis of the frame 2; and then, the key ring 18 is fixed on the frame 2 by using an adhesive or the like. The key 20, which faces the tip side of the frame 2, engages with a key groove 23 of the optical connector adaptor 22 (see FIG. 9), and positioning the optical connector 1 and the optical connector adaptor 22.
When, for example, a pair of optical connectors 1 of this constitution are connected on both sides of a conventional optical connector adaptor 22, as shown in FIG. 9, the thrusting connection between the ferrules 8 optically connects the optical fibers of the optical connectors 1. That is, to connect the optical connectors 1 to the optical connector adaptor 22, the frame 2 and ferrule 8 of each optical connector 1 are inserted into the sleeve section 22a of the optical connector adaptor 22, the key 20 of the key ring 18 is inserted and engaged with the key groove 23 of the optical connector adaptor 22, and the coupling nut 6 of the optical connector 1 is screwed into the male screw section of the sleeve section 22a (see FIG. 9) of the optical connector adaptor 22. Consequently, the ferrules 8 which are held in position inside the frames 2 of the optical connectors 1, connected via the optical connector adaptor 22, and are thrust together and precisely positioned and connected on the same straight line by a positioning mechanism such as a positioning sleeve inside the optical connector adaptor 22. Furthermore, the positioning of each ferrule 8 of the optical connectors 1 around the axis thereof is performed by engaging the keys 20 of the key rings 18 with the key grooves 23 of the optical connectors 1.
In this type of optical connector 1, the position of the optical fiber (more specifically, the core of the optical fiber) which is securely inserted into the ferrule 8 is adjusted (more specifically, its position with respect to the frame 2 is adjusted) and centered so as to keep connection loss sufficiently low. In this case, the frame 2 and the optical fiber inside the ferrule 8 are centered by, for example, adjusting their relative positions by using a monitor device so that the meshing grooves 10 of the flange section 9 meshes with the meshing pieces 11 of the frame 2, and minimizing the connection loss between the optical fibers when the optical connectors 1 and 1 are connected via the optical connector adaptor 22. When the optical connectors 1 assembled in this manner are connected via the optical connector adaptor 22, the optical fibers which are securely inserted into the ferrules 8 of the optical connectors 1 are thrustingly connected with low connection loss.
When this type of optical connector 1 is used in connecting a PMF (Polarization-Maintaining optical Fiber, PANDA elliptical-clad, PANDA: Polarization-maintaining AND Absorption-reducing fiber), or when an APC (Angled Phase Contact) polished-type ferrule is used, and in other such cases, the optical connected must be positioned with high precision; however, due to specifications dependent on the manufacturer, the type of ferrule, and the like, the size of the key of the optical connector 1 may be different from the size (groove width) of the key groove of the optical connector adaptor 22 which in the optical connector 1 is to be connected to, making it necessary to carefully select the optical connectors and optical connector adaptor to be used; this is inconvenient.
Furthermore, the dimensions of the key groove of the optical connector adaptor and the key of the optical connector are held to closer tolerances in order to increase the positioning precision at the time of connection. However, this requires ultra-precise machining, and the cost of which exceeds the cost of the optical connector.
In addition, in the case of an FC-type optical connector, the optical connector is fastened to the optical connector adaptor by screwing (the screwing of the coupling nut as described above); when there is a slight clearance between the key and the key groove (i.e. when high positioning precision is not required), the rotation of the screw (coupling nut) at the time of attaching and removing the optical connector to and from the optical connector adaptor causes the key to move in the key groove. Since this may adversely affect the optical fiber and the ferrule, such as by damaging the tip of the optical fiber which is exposed at the top of the ferrule, there is a demand for techniques to reliably prevent such damage.